Ah, so this is what a frozen battery feels like

[Bob64]

Whoo, with the temps dipping way below freezing in VA, I've noticed more pronounced behavior that I've never noticed before (well, at least since I got the scangauge). Gosh its so cold, it hurts to breathe! (I think the insides of my lungs are freezing).

When I first turn on the car, the coolant temp is (2 degrees C) according to the scangauge.

At these temps, the coolant thermos doesn't even make a dent in the temp of the coolant.

Acceleration feels like it doesn't use the battery at all. The engine starts much more easily (like if your on 3 bars) at the slightest press of the accel.

Regeneration appears to be limited to approx 30amps. (must be due to the battery not reaching operating temp).

With a blocked grill, the water temp never appears to go above 83c even though the engine is running, I wonder if the thermostat is opening or if the fans are spinning (hope not, im freezing my ass off in the car!)

I think I might turn on the heat a bit when the temps reach above 80c.


I guess I've always taken it for granted that normal temps around here are a lot warmer then what we've been experiencing recently... and its killing my mileage! Between the longer time that it takes me to get into stage 4 (if at all!), the idling at speeds under 35mph (while not in stage 4), the reduction of regeneration voltage, winter gas, winter air density... It has knocked down my ~64mpg "cold" winter daily average to a freezing ~55mpg or so.

Blah, I miss the summer, where I can get 70+mpg :/

[Mjolinor]

Obviously Prius owners need to learn how to hibernate.

Tip, learn it from a bear, not from Windows.

[JimboK]

Tell me about it! Yesterday was my first sub-60 MPG day of normal commuting in a long time. (I probably still would have kept it above 60 if not for an essential 1-mile trip at lunchtime.)

I first noticed this behavior on some of our coldest days last winter. The most noticeable effect for me, in addition to what you've described, was that EV mode (with the switch) was denied. After some dialog with other EV users, it seems that low temperatures and, in particular, low battery temperatures are an "EV-deny" criterion, though one that seems missing from most EV-deny criteria lists.

I didn't pay much attention to battery temperatures last year because last year's severe cold snap was short and, compared to this one, relatively mild. This year I've been watching it, and it appears that 35F is the critical threshold. I'd be interested in hearing from other EV switch users who monitor battery temp.

So we're between a rock and a (frozen) hard place: Using the battery will warm it up, but a cold battery won't allow itself to be used. So what I've found myself doing the last day or two is seeking somewhat different routes early in the commute where the ICE would have to run anyway for propulsion, allowing the shortest warmup time possible. After the ICE hits 157F, normal S3 and S4 behavior occurs, including ICE shutdown. I find myself actually approaching red lights rather quickly to allow time to stop for the S4 idle routine; normally I time them to avoid stopping. Good thing is, by then, I've got SOC levels often at 70% or above, so I can do some pretty good runs of pedal-feathered EV at 34-40 MPH in S3 and all speeds below 40 in S4. With that, the battery seems to warm up pretty quickly, though I still can't use the EV switch until it hits 35F or so.

Today's commute will be interesting. It's 5F right now -- the coldest it's been in these parts in five years.

[paprius4030]

It's -13 F here in the Poconos this am. Think it's the coldest ever since I've had a Prius. Instead of watching the mpg's I watch when it's warm enough for the heater blower fan to come on LOL.

[Mike Dimmick]

Turn the blower on yourself, and you should get the assistance of the electric heaters in the heater core and footwell, if the engine coolant temperature is below 55 celsius (and your car has them - apparently only fitted in 'cold regions'). There are a pair of PTC HTR relays in the centre relay box in the engine compartment, and corresponding 30A fuses in the right-hand-side (as you stand in front of the car) fuse/relay box which control the two heaters in the heater core, and a PS HTR relay next to the PTC HTR relays and a 50A fuse that control the footwell heater.

There's no point freezing to death in the car - turn the heating on and it will warm up the HV battery at the same time it warms you up. Battery chemistry is subject to temperature.

This chart comes from Panasonic EV Energy's webpage:



At a comfortable 20 degrees Celsius, the specific power is more than twice that at freezing temperatures (0 Celsius) and four times that at -10 degrees C (14F).

Much like the catalytic converter pre-heating, it's a trade-off between consuming more fuel immediately after starting up for better economy later on.

[paprius4030]

The heater blower clicks on the first setting after only a few minutes so I always figured it did that by itself when the electric heater started making enough heat??? There's no way the coolant could be warm enough that soon, I have to check it with my new scan guage though

[JimboK]

Well, I managed 64 MPG on the way in this morning. Light weekend traffic meant fewer red lights, and by the time I got to the first one I was up to 157F, so I could get it into S4. Good thing too, because the battery temp started at 24F and got only as high as 33F; the EV button never worked.

Originally Posted by Mike Dimmick

There's no point freezing to death in the car - turn the heating on and it will warm up the HV battery at the same time it warms you up. Battery chemistry is subject to temperature.

You seem to be making the assumption that those of us concerned with battery temperature are also concerned with body temperature.

Seriously, it is fuel economy fanatics, not drivers trying to warm themselves, that are concerned about battery temperature. Some of us are so obsessed that we keep the cabin heat off in the coldest of weather. On my commute, the car will never make it to S3/S4 temperatures in this weather if the cabin heat runs. Which means, effectively, that the ICE will never shut off unless I'm at a complete stop.

True, cabin heat will help warm the battery to allow EV, but the battery is a large thermal mass and radiant heating (and cooling) is pretty slow. I won't have EV available anyway in the first few minutes of warmup, so I'm concerned more about warming the ICE than warming the battery. I don't care if I can't run on the battery if I can get the ICE to shut off when it's not needed for propulsion.

Meanwhile, I'm not freezing to death. I bundle up pretty thoroughly.

[dogfriend]

Originally Posted by Bob64

With a blocked grill, the water temp never appears to go above 83c even though the engine is running, I wonder if the thermostat is opening or if the fans are spinning (hope not, im freezing my ass off in the car!)

I think I might turn on the heat a bit when the temps reach above 80c.

The thermostat opening temp is 82°C (nominal).

[Mjolinor]

Does the rear O2 sensor report temperature? If so then lagging the cat to keep it's heat in may help reduce the engine running time.

[Bob64]

I think an O2 sensor only reports oxygen content.... otherwise it'll be called a temperature sensor.

I guess I'm going to have to start using the heat more often then. No point in wasting it by letting it radiate away.

Anyone know what temp the radiator fan start turning on?